The present invention relates to a pattern formation method employed in semiconductor fabrication process.
In accordance with the increased degree of integration of semiconductor integrated circuits and the downsizing of semiconductor devices, development of lithography technique is desired to be accelerated.
At present, patterns are formed through photolithography using a mercury lamp, KrF excimer laser or ArF excimer laser as exposing light. In order to form a fine pattern of 0.1 μm or less and particularly 50 nm or less, extreme UV of a wavelength (of a 1 nm through 30 nm band) shorter than that of the aforementioned exposing light is desired to be used as the exposing light. This is because a highly productive pattern formation method using exposing light is desired to be prolonged in its life.
Also, in using extreme UV as the exposing light, a chemically amplified resist material with high resolution and sensitivity is preferably used.
Now, a conventional pattern formation method using extreme UV as the exposing light will be described with reference to FIGS. 5A through 5D.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((2-methyl-2-adamantyl acrylate) − (γ-2gbutyrolactone methacrylate)) (wherein 2-methyl-2-adamantylacrylate:γ-butyrolactone methacrylate = 60 mol %:40 mol %Acid generator: triphenylsulfonium triflate0.04gSolvent: propylene glycol monomethyl ether acetate20g
Next, as shown in FIG. 5A, the chemically amplified resist material is applied on a semiconductor substrate 1, so as to form a resist film 2 with a thickness of 0.2 μm. Thereafter, the resist film 2 is pre-baked.
Then, as shown in FIG. 5B, pattern exposure is performed by irradiating the pre-baked resist film 2 with extreme UV 3 (of a wavelength of a 13.5 nm band) output by a laser plasma light source and having exposure power of 10 W and exposure energy of 20 mJ/cm2 selectively through a reflection mask not shown.
Thereafter, as shown in FIG. 5C, the resist film 2 having been subjected to the pattern exposure is subjected to baking 4 at a temperature of 100° C. for 60 seconds with a hot plate. Thus, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer owing to a function of an acid generated from the acid generator while an unexposed portion 2b of the resist film 2 remains insoluble in an alkaline developer because no acid is generated therein.
Subsequently, as shown in FIG. 5D, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer (alkaline developer), so as to form a resist pattern 5 with a line width of 0.07 μm.
As shown in FIG. 5D, however, the resultant resist pattern 5 is degraded in its cross-sectional shape. When the shape of the resist pattern 5 is thus degraded, a failure is caused in a pattern formed by using this resist pattern 5 as a mask, resulting in lowering the yield in the semiconductor process.